The present invention relates to a method of controlling a write operation for a rotating type recording medium, and more particularly to a write operation control method suitable for use in an erasable optical disc.
Recently, with the advance in information processing techniques, the amount of data processed by a data processor has been greatly increased. Thus, an optical disc which can store a large amount of data at a high recording density has been drawing attention. In an optical disc apparatus, a light beam emitted from a laser light source is focussed to a light spot having a diameter of 1 to 2 .mu.m, and the thermal change of that portion of a recording film which is irradiated with the light spot, is used for recording information in the recording film. Further, the recorded information is reproduced in such a manner that the recording film is irradiated with a light beam having a relatively weak intensity, and the difference between the intensity of light reflected from a film portion which has been subjected to the above thermal change and the intensity of light reflected from an ordinary film portion is detected.
As described on pages 189 to 213 of the Nov. 21, 1983 issue of the "NIKKEI Electronics", for example, an optical disc apparatus in which a metal film made of a ternary alloy Pb-Te-Se is used as the recording film and laser light of high power is used in the information recording operation to form a data pit having a diameter of about 0.8 .mu.m in the recording film, has been put to practical use, as an optical disc apparatus capable of recording and reproducing code information, picture information and document information which are processed by the data processor. In such an optical disc apparatus, the irreversible change of the recording film is utilized to record information in the recording film, and hence information having been recorded in the recording film cannot be rewritten. Accordingly, in the case where it is necessary to rewrite the recorded information, the following processing is carried out. That is, in the above optical disc apparatus, a region for storing flag information is provided in each block which constitutes a recording/reproducing unit, a flag indicating that information recorded in a block is ineffective, is recorded in the flag region of the block, to theoretically or logically erase the recorded information, and another block on the recording film is specified to write new information in the specified block.
Two kinds of optical discs have been known in which the reversible change of a recording film is utilized to write information in a block and to erase information recorded in the block.
The optical disc of the first kind is called a photo-magnetic type optical disc. In the photo-magnetic type optical disc, a thin magnetic film having the axis of easy magnetization perpendicular thereto is used as the recording film, and information is recorded in the magnetic film by irradiating the magnetic film with laser light in a state that an external magnetic field opposite in direction to the axis of easy magnetization is applied to the magnetic film. That portion of the magnetic film which is irradiated with the laser light, is locally heated. When heated to a Curie temperature, the portion is demagnetized. When the temperature of the portion returns to ordinary temperature, a reverse magnetic domain having the same direction as the external magnetic field is formed at the portion, and is used as the information recording bit. Information recorded in the magnetic film is reproduced by utilizing the phenomenon that it depends upon the direction of magnetization at a light receiving portion whether the polarization plane of light reflected from the light receiving portion rotates clockwise or counterclockwise, that is, by utilizing the magneto-optical effect. Further, the erasure of recorded information is carried out in such a manner that a portion of the magnetic film where information has been recorded, is heated by laser light to the Curie temperature, while applying an external magnetic field having the same direction as the axis of easy magnetization to the magnetic film. The magnetic film of this kind may be made of, for example, a ternary alloy Tb-Fe-Co or Dy-Fe-Co which is proposed in Japanese patent application unexamined publication No. 58-73746.
The optical disc of the second kind utilizes the reversible state change of a recording material due to laser light. For example, as proposed in the Japanese Examined Publication No. 47-26897, an optical disc utilizing the phase transition between the crystalline phase and amorphous phase of the recording film, is typical of optical discs of the second kind.
For such an optical disc, recording, reproducing and erasing operations are performed in the following manner. In the recording operation, a portion of the recording film, assuring the crystalline phase is irradiated with laser light is rapidly cooled to put the portion having small light reflectivity in the amorphous phase. Information recorded in the recording film is reproduced by utilizing the difference in reflectivity between the crystalline portion and amorphous portion of the recording film. Information recorded in the recording film can be erased by heating the recording film and then cooling it slowly.
In a case where a write operation is performed for an erasable optical disc, blocks where information is to be recorded on the basis of write instructions from an upper apparatus, includes a block where information has been recorded wherein an erasing operation is necessary for writing new information, and a block where no information has been recorded and hence desired information can be immediately recorded. In the above case, if a write operation according to a recording mode including an erasing operation, is carried out for each of the write instructions, the erasing operation will be performed even for a block where no information has been recorded. In the recording mode for recording new information in a block after recorded information in the block has been erased it is necessary to first wait for the positioning of the optical head on a desired block three times, that is, before the erasing operation for erasing information which has been recorded in the block, before the write operation for writing new information in the block, and before the read-after-write operation for checking the new information recorded in the block. If such a recording mode is used for all the blocks where information is to be recorded, the efficiency of the write operation for these blocks will be reduced. In the case where the high-ranking apparatus issues an erase instruction only for each of the blocks where information has been recorded, before the write operation, in order to reduce the loss of time, it will be necessary for the high-ranking apparatus to be well aware of the state of every block on the optical disc, thereby placing a heavy burden on the high-ranking apparatus.